1. Field of the Invention
The invention relates to a fuel injection device for a diesel internal combustion engine. The fuel injection device includes an injection nozzle connected to a fuel injector through a pressure line. The fuel injector has a housing with at least one fuel line for the inflow and outflow of fuel, a pump chamber, and a plunger. The plunger has at least one annular groove with two control edges fluidly connected with the pump chamber. The housing has a relief passage for interrupting pressure build-up in the pump chamber.
2. Description of the Prior Art
It is known that fuel injection devices are used in internal combustion engines, in which the main injection phase is preceded by a preinjection phase, are used in internal combustion engines Thus, the load on the engine parts is reduced and the combustion process in the internal combustion engine is improved U.S. Pat. No. 4,426,198 discloses such an injection device The injection device disclosed in U.S. Pat. No. 4,426,198 includes a plunger with an oblique control edge. The plunger is driven by a camshaft. The injector housing is provided with a fuel chamber, into which open inlet passages for the fuel, and from which a pressure line leads to the injection nozzle. The end surface of the plunger and edges of a first annular groove on the periphery of the plunger form control edges, and cooperate in a known manner with the inlet passages. A second annular groove, is connected with the fuel chamber and is located below the first annular groove with an oblique edge. The second annular groove is also connected with the fuel chamber. A relief passage is fluidly connected with the outlet line for fuel With the beginning of the injection cycle, the inlet line for fuel and the relief passage are closed by the plunger, and pressure builds up in the fuel chamber. This pressure drops again as soon as the lower groove opens the relief passage, by which the injection cycle is interrupted. The duration of the interruption depends on the dimensions of the second groove and the speed of movement of the plunger. The interruption takes place at a moment at which the plunger already has a relatively high speed. The camshaft accelerates and moves the plunger farther, and movement of the plunger is wasted. So that the fuel in the fuel chamber can flow out, the groove and the relief passage must have relatively large dimensions, which leads to increased leakage.
As soon as the relief passage is closed again a pressure surge results from the high plunger speed and is transmitted to the camshaft which can lead to additional harmful loads on the camshaft. The high forces, caused by the pumping pressure, for example, at 2000 bar injection pressure, cause torsional vibrations as a result of pressure line deviations, which displace the beginning of injection dynamically by several degrees crank angle. With high plunger speeds, and especially with high speed engines, other disadvantages occur, such as, the relief passage being passed over so quickly by the second groove that the drop of pressure no longer takes place correctly. In large engines, the forces acting on the camshaft are so great that special measures are necessary and the construction of shafts and cams becomes very expensive. The forces acting on the camshaft and the speed of movement of the plunger limit the stroke distance of the plunger and also the maximum pressure which can be produced in the fuel chamber.